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From |
"Nick Cox" <n.j.cox@durham.ac.uk> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: Question about cumulative density (cumul, xtile) -- quintiles and poverty status are not in sync. What am I doing wrong? |

Date |
Fri, 3 Aug 2007 18:40:59 +0100 |

I have thoughts on various levels. Others can advise better on survey statistics, the quantum mechanics of statistics, in which thinking you understand probably means you are not confused at a high enough level. 1. I see that you are using -cumul- with -aweight- and -xtile- with -pweight- and I would have thought it quite likely that that would be a source of difficulty. I know that -cumul- doesn't support -pweight-, but ignoring that problem won't be a solution. -cumul- itself is not a big deal; so as long as you can define the cumulative for a set of values with associated pweights, its computation should be easy, using -sum()- to cumulate. 2. You reported problems with -xtile2-. Please say where user-written programs you are using come from. -xtile2- is a user-written program from SSC. It gives you the error you report, I surmise, because it lacks a -version- statement and so is broken by a later change in Stata's syntax. This issue was discussed at length in a recent thread on -outreg2-. I think you need to insert version 7 after the -program- statement. 3. I think that the term "cumulative distribution function" is more nearly standard. I know that a density function is integrated to get a distribution function, but the result is no longer a density. Anyway, literatures may differ, but my impression is that cumulative density is not a standard term. 4. Code like gen quint=1 if cumdens<=.2 replace quint=2 if cumdens>.2&cumdens<=.4 replace quint=3 if cumdens>.4&cumdens<=.6 replace quint=4 if cumdens>.6&cumdens<=.8 replace quint=5 if cumdens>.8&cumdens~=. could be condensed to this gen quint = ceil(5 * cumdens) Here -ceil()- short for "ceiling" rounds up to the nearest integer. Also there is need to trap missings. -ceil()- is discussed in SJ-3-4 dm0002 . . . . . . . . Stata tip 2: Building with floors and ceilings Q4/03 SJ 3(4):446--447 (no commands) tips for using floor() and ceil() and again in "33 Stata Tips" available from StataCorp in paperback. Nick n.j.cox@durham.ac.uk Anna Gueorguieva > My quintiles and poverty status do not seem to be in sync and > I have no idea what is going on!! > > I generate my indicator for poor as having consumption per > adult equivalent below the poverty line. > gen poor=real_totc_per_ae<=povline_m > > Then I generate my quintiles by creating a cumulative > distribution of consumption (in each survey wave) > I use xtile and then double check it with the cumulative density. > > foreach x of numlist 1/4{ > xtile quint`x'= real_totc_per_ae [pw=postpweight] if wave==`x',nq(5) > } > gen quint=quint1 > foreach x of numlist 1/4{ > replace quint=quint`x' if wave==`x' > } > > bys wave: cumul real_totc [aweight=postpweight], gen(cumdens) > > *check quints > replace quint=1 if cumdens<=.2 > replace quint=2 if cumdens>.2&cumdens<=.4 > replace quint=3 if cumdens>.4&cumdens<=.6 > replace quint=4 if cumdens>.6&cumdens<=.8 > replace quint=5 if cumdens>.8&cumdens~=. > And the problem is below -- it is not possible that there are > poor people in quintile 3!!!! : > tab quint poor [aw=postpweight] if wave==2, col nof > Quintile | > of | > national | > distributi | poor > on | 0 1 | Total > -----------+----------------------+---------- > 1 | 0.00 45.96 | 19.98 > 2 | 0.40 45.44 | 19.98 > 3 | 28.81 8.61 | 20.03 > 4 | 35.19 0.00 | 19.89 > 5 | 35.60 0.00 | 20.12 > -----------+----------------------+---------- > Total | 100.00 100.00 | 100.00 > > And xtile2 gives me an error: > xtile2 newquint=real_totc_per_ae [pw=postpweight] ,nq(5) by(wave) > program error: matching close brace not found > r(198); * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: RE: Question about cumulative density (cumul, xtile) -- quintiles and poverty status are not in sync. What am I doing wrong?***From:*"Austin Nichols" <austinnichols@gmail.com>

**st: RE: RE: Question about cumulative density (cumul, xtile) -- quintiles and poverty status are not in sync. What am I doing wrong?***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

**References**:**st: Question about cumulative density (cumul, xtile) -- quintiles and poverty status are not in sync. What am I doing wrong?***From:*Anna Gueorguieva <anna_i_g@yahoo.com>

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